Field of the Invention
The present invention relates to an outer case molding method in an electronic circuit unit applied, for example, to an electronic control unit (ECU) or the like for an automobile, in particular, in the electronic circuit unit in which an outer case formed by mold resin is formed integrally with a circuit board.
Description of Related Art
In a case where a circuit board (a printed wiring board, a bus bar wiring board or the like) mounting electronic components thereon is modularized as a single electronic circuit unit equipped with a connector, etc., in general, the electronic circuit unit has been configured by incorporating the circuit board into a hard case made of resin molded separately (see a patent literature 1: JP-A-2000-134766).
However, in a case where the electronic circuit unit is configured in such the manner, the number of the components and a cost of the assembling become large.
Thus, it has been considered to set a circuit board mounting electronic components thereon within a die and form an outer case by thermoplastic resin according to insert molding. In a case of forming the outer case by the mold resin according to the insert molding in this manner, it is not necessary to separately mold a hard case by resin and incorporate the circuit board within the hard case. As a result, the number of the components can be reduced and the assembling work can be eliminated advantageously.
[Patent Literature 1] JP-A-2000-134766
According to a related art, in setting a circuit board within a die and molding a outer case, it is required not to apply a pressure against electronic components (for example, an electrolytic capacitor, an oscillator, a filter, etc.) which are intolerant of a pressure of a resin (in particular, a filling pressure of the resin into the die) upon a molding.
In terms of this, consideration is made that the electronic components intolerant of a pressure of the resin upon the molding are collectively arranged at a particular portion on the circuit board, then the circuit board is set in the die in a state of exposing the particular portion outside the die, and the outer case is formed by injection molding.
However, if the outer case is molded in this manner, the circuit board may be deformed due to a pressure of the resin acting on a rear surface side of the exposed portion upon the molding, and hence conductor wiring patterns, etc. of an inner layer of the board may be damaged.
The invention is contrived in view of the aforesaid circumstances and an object of the invention is to provide an outer case molding method in an electronic circuit unit which can suppress damage of a circuit board and electronic components caused at a time of forming the outer case by injection molding.